It is known from the prior art that a pyrolysis product, i.e. pyrolysis liquid or pyrolysis gas, is produced from different kinds of biomasses or organic materials such as wood, bark, paper, straw, waste plastic, oil shale, lignite, peat or the like by dry distillation with the pyrolysis technique. The pyrolysis is typically performed in oxygen-free conditions at a temperature of about 300 to 800° C. When slow heating rate is applied, the pyrolysis liquid, e.g. wood tar from dry wood, can typically be recovered in an amount of about 20 to 30% by weight. The amount of the pyrolysis liquids is increased when higher heating rates are applied. There are many known fast pyrolysis methods for producing pyrolysis products and chemicals.
Fast pyrolysis is typically carried out by heating the fuel to be pyrolyzed in a hot oxygen-free environment by introducing the required heat to the pyrolyzer by means of a heating gas, heat exchanger, heat transfer agent, e.g. sand or aluminum oxide based carrier, or catalyst. For example a bubbling or sand circulating fluidized-bed reactor may be used as the pyrolyzer. The produced pyrolysis vapor is typically condensed to a temperature of less than 100° C. in order to form the pyrolysis liquid.
The fuel to be pyrolyzed, e.g. biomass, is usually conducted to a dryer before the pyrolyzer for drying in order to reduce the water content of the pyrolysis liquid that is being formed. Typically drum, belt, flash or fluidized-bed dryers are used. It is also known to use a steam dryer in which the heat is introduced by means of hot sand to the dryer operating on the fluidized-bed basis and in which only water is removed. The temperature is kept at such level that organic compounds do not escape.
From WO 2009047392 is known an apparatus for producing a pyrolysis product in which a pyrolysis reactor and a boiler are integrated.